The field of microfluidics has rapidly emerged and has been implemented in an array of applications, such as molecular analysis, bio-defense, molecular biology, microelectronics, and the like. In the field of microfluidics, microvalves may be used to control the routing, the timing, and the separation of fluids in many different microfluidic systems.
Some microvalves deploy electrokinetic actuation to displace fluids from one microfluidic channel to another microfluidic channel. The mechanism of electrokinetic microvalves is simple. However, such electrokinetic microvalves demand a dielectric substrate, which is strongly influenced by the ionic composition of the fluid, high-voltage sources and switches, and a continuous buffer flow to enable microvalve functions. The next generation microvalves, such as Quake microvalves and plunger microvalves, are able to avoid cumbersome, high-voltage sources and switches. However, these microvalves generally rely on the deflection of a Poly(dimethylsiloxane) (PDMS) membrane to interrupt the flow of fluid. Due to the integration of the control channel within the microfluidics channel on the same PDMS chip, the device structures and fabrication may be complicated. Lateral-deflection membrane microvalves simplify the fabrication, but impose an intrinsic undesirable effect of leakage of the channel. Other “doormat” and “curtain” style microvalves inherently risk permanently bonding the microvalve closed during assembly. This risk may be mitigated by adding a non-PDMS valve seat, but the addition of a non-PDMS valve seat incurs the trade-off of fabrication complexity. Along with these aforementioned challenges, pneumatic microvalves also require external pneumatic elements. Other than these pneumatic microvalves, pinch microvalves directly exert mechanical force on the PDMS bulk that forms the device, which is straightforward, yet an ample distance between adjacent pinching points needs to be provided. Entirely different from microvalves controlled by physical forces, phase-change microvalves control the flow of fluid through a solid and fluidic phase modulation. However, these phase-change microvalves require an additional cooling or heating element. Additionally, the phase modulation of these phase-change microvalves induce a slow actuation of approximately 1 to 10 minutes. Noteworthy burst microvalves and bubble microvalves incorporate innovative actuations but are hard to control. Additionally, burst microvalves and bubble microvalves may contaminate the samples in the microfluidic channel.